1. Field of the Invention
The present invention relates generally to the fields of Couette devices and methods involving their use. More particularly, it concerns Couette devices capable of imparting fully turbulent flow to samples, such as crude oil samples, for use in measuring deposition of solids from the samples.
2. Description of Related Art
In fluids which it is desirable to transport by flowing through pipes or tubing, the deposition of solids from the fluid onto the interior walls of the pipes or tubing can impair fluid flow. An example of such a fluid is crude oil. Crude oil from many formations commonly contains solids, often as one or more of waxes, asphaltenes, sulfur, scale, and hydrates.
Paraffin waxes are essentially mixtures of long-chain n-paraffins with carbon chain lengths ranging from C15 to C75+.
Asphaltenes and residual oil components often co-precipitate with the paraffin waxes and result in varying appearance (color) and texture to the precipitated solids. Asphaltenes are generally compounds comprising more than about 70 carbon atoms, mostly in aromatic polycyclic clusters variably substituted with alkyl groups; asphaltenes can also contain heteroatoms (such as N, S, or O), metals (such as Ni, V, or Fe), or both.
Hydrates generally comprise water molecules in an ice-like structure encaging one or more organic compounds. The organic compounds encaged by the ice-like structure are commonly methane, ethane, propane, or other alkanes with less than about 10 carbon atoms.
Under many conditions, the solids present in a fluid will remain dissolved in the fluid. However, when a fluid, such as crude oil, is transported via pipe, such as from a geologic formation to a wellhead via production tubing or from a wellhead or a storage vessel to a refinery via a pipeline, changes in the pressure, temperature, composition, or other parameters of the flowing fluid can lead to precipitation and deposition of solids. Deposition in a pipe is generally undesirable, because deposited solids can at least partially block the pipe and lead to reductions in the flow rate of the fluid in the pipe and require expensive and time-consuming cleaning of the pipe to restore the maximum flow rate of the fluid.
Similar observations exist for other fluids which can contain solids. Such fluids, either liquids or gases, include fluids used in the industrial production of paint, food products, pharmaceuticals, plastics, and paper and paper products, among other industries.
The study of deposition is difficult for, among other reasons, the difference between fully turbulent flow (that is, flow that is both non-laminar and without the presence of vortices) of a sample fluid in a pipe and the sample fluid in a laboratory scale apparatus. Common laboratory scale apparatus are generally unable to provide conditions for fully turbulent flow as a result of limitations in apparatus geometry and design. Further, common laboratory scale apparatus generally cannot provide sufficient levels of pressure and shear to readily study the deposition of solids.
Therefore, it would be desirable to have apparatus and methods for analyzing deposition of solids that can simulate the turbulent flow found in production tubing or pipeline under field conditions.